It is frequently desirable to provide relatively easily assembled and disassembled ground overlays of a load-carrying nature to form landing and take-off strips, roadways and surfaces upon which machinery or equipment can be mounted, without the need for fabricating a massive substructure of concrete or like surfaces.
For this purpose, steel overlays formed from a multiplicity of substantially identical elements, can be assembled in the field and, once the need has disappeared, can be disassembled and removed.
Such overlays are primarily used for the landing and take-off of aircraft and are commonly referred to as landing mats. They can be applied over all or a portion of a generally flat strip of terrain, preferably a strip which has been at least somewhat stabilized by precompaction, and the elements of the landing mat can be rectangular units which are joined in contiguous relationship.
As described in German patent document 23 45 457, for example, each unit or element is formed with a plurality of welded ribs or flanges extending parallel to the longitudinal edges of the rectangular element.
Apart from being inordinately expensive, at least in part because of the labor-intensive fabrication technique resulting from the need to weld the ribs or flanges in place, difficulties have been encountered with such elements or units because the forces applied to the landing mat tend to apply stresses to these elements which can break the connection between the platform forming the upper surface of the element and the downwardly extending ribs or flanges welded thereto. However, the ribs and flanges have been found to be essential to prevent buckling or distortion of the upper surface upon which the aircraft may have to land.